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Thursday, November 16, 2006

Nichia hits 138 lm/W


Nichia has developed LEDs with indium tin oxide contacts that can deliver an efficacy of 138 lm/W and an output of 402 lumens at 2A.

Japanese LED chip manufacturer Nichia has produced a small white-emitting LED chip that has an efficacy of 138 lm/W at 20 mA, and a larger device that delivers 92 lm/W at 350 mA.
The small chip, which measures 240x420 ┬Ám, has a color temperature of 5450K, a wall plug efficiency of 41.7%, and a forward voltage of 3.11 V at 20 mA.
The 1x1 mm chip has a slightly lower color temperature and efficacy, but can deliver 106 lumens at 350 mA and 402 lumens at 2 A, which is equivalent to the total flux of a 30 W incandescent lamp.
Both of the MOCVD-grown devices produce white light by exciting a yellow YAG phosphor with 450 nm emission from an InGaN/GaN LED. The high efficacy of the chips results from improvements in external quantum efficiency, according to Nichia's researchers.
The LEDs do not use a conventional translucent Ni/Al p-contact that has a transmittance of only 40%, but instead employ an indium tin oxide electrode with a transmittance of 95%.
Extraction efficiency is also boosted by growth on a sapphire substrate patterned with convex hexagons, which scatter more of the light emitted from the active layer.
Nichia's results compare favorably with those of Cree, which reported a white LED chip delivering 131 lm/W at 20 mA this summer. Nichia's results were obtained using pulsed operation (200 Hz repition rate, and a duty cycle of 1 %). Cree provided no details of its mode of operation.

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